Known as one of techniques for directly producing a strip from molten metal is twin-roll continuous casting where molten metal is supplied to between a pair of rotated rolls to deliver a solidified metal strip therefrom.
FIG. 1 shows a convention twin roll caster comprising a pair of chilled rolls 1 arranged horizontally side by side and a pair of side weirs 2 associated with the rolls 1.
The chilled rolls 1 are constructed such that cooling water passes through the rolls and a nip G between the rolls may be expanded/contracted depending on thickness of the strip 3 to be produced.
The rotated speed and direction of the chilled rolls 1 are set such that outer circumferential surfaces of the respective rolls move from above to the nip G between the rolls at the same speed.
One of the side weirs 2 surface-contact one ends of the respective chilled rolls 1 and the other side weir 2, the other ends of the rolls 1. In a space defined by the chilled rolls 1 and the side weirs 2, a molten-metal delivery nozzle 4 made from refractory material is arranged just above the nip G between the rolls.
The delivery nozzle 4 has a top with an elongated nozzle trough 6 for receiving molten metal 5 and has longitudinal side walls formed with openings 7 from the trough 6 toward the outer circumferential surfaces of the chilled rolls 1, the openings 7 being formed on the side walls adjacent to lower ends thereof and being aligned along axes of the rolls 1. When the molten metal is poured into the nozzle trough 6, a casting pool 8 is formed above the nip G between the rolls 1 and in contact with the outer circumferential surfaces of the rolls 1.
Thus, with the casting pool 8 being formed, the rolls 1 are rotated while being cooled by circulation of cooling water, so that the molten metal 5 is solidified on the outer circumferential surfaces of the rolls 1 to deliver a strip 3 downwardly from the nip G.
In so-called triple point regions where the rolls 1, the side weirs 2 and the casting pool 8 meet, the solidified shells may be produced abnormally.
If such solidified shells at the triple point regions were drawn and peeled away by the solidified shells on the outer circumferential surfaces of the rolls 1, they might be drawn into the nip G between the rolls 1, resulting in not only defective shape in the form of locally thickened strip 3, but also deteriorated cooling efficiency due to the flared nip G by the locally thickened strip, breakage of the strip 3 due to thermal recuperation from the molten metal 5 and/or impair of the side weirs 2 upon drop of the solidified shells.
Thus, a twin roll caster has been proposed which directs molten metal 5 to side weirs 2 and especially positively in a direction tangent to chilled rolls 1 so as to suppress formation of undesired solidified shell (see, for example, Patent Literature 1).
[Patent Literature 1] JP62-45456A